Introduction. In October 2010, an outbreak of foodborne illness affecting students at several middle schools in Poitiers was reported. The environmental investigation identified the causative agent—Salmonella—as well as the source of contamination: frozen ground beef. A follow-up study was conducted to describe and assess the extent of the salmonellosis outbreak as well as the characteristics of the cases occurring in schools. Methods. A retrospective cohort study was conducted using a self-administered questionnaire among all individuals attending one of the four schools that received a batch of the implicated frozen ground beef and reported at least one case of illness. All Salmonella strains identified by laboratories in Poitiers were analyzed by the National Reference Center for serotyping confirmation. Results. The survey response rate was 86%. The survey identified 558 cases in school settings, 25 of which were biologically confirmed; 4 cases were identified solely based on microbiological analysis. Thirty-one cases were hospitalized for more than 24 hours, and no deaths occurred. Adults were at lower risk than adolescents. The identified serotype of salmonellosis was strain 4,5,12:i. The overall attack rate was high (35%) and varied significantly among schools (range: 17% to 47%). The median incubation period (34 hours) was shortest in the middle school with the highest attack rate. Conclusion. Contamination of frozen ground beef was the cause of a large-scale outbreak of Salmonella enterica salmonellosis in a school setting. This is the first time that serotype 4,5,12:i has caused a widespread, reported foodborne illness outbreak in France. The rapid identification and recall of the implicated batch likely helped limit the extent of the outbreak. (R.A.)